Atomic layer deposition (ALD) is a vapor phase technique capable of producing thin films of a variety of materials. Based on sequential, self-limiting reactions, ALD offers exceptional conformality on high aspect structures, thickness control at the Angstrom level, and tunable film composition. As a result ALD may be applicable for many industrial applications.
Atomic layer deposition (ALD) has been used in the semiconductor industry for a decade or more. The process works by first adsorbing a (mono) layer of a precursor on a surface of a sample, purging the excess precursor, and then introducing a second reactant which converts the adsorbed layer to the desired chemistry. This results in non-line of sight (NLOS) deposition of uniform, pinhole free, conformable, ultra-thin, coatings with low residual stress. The reaction conditions are chosen to achieve the best combination of precursor adsorption and subsequent reaction, with very low reaction temperatures (typically less than 700° C.) and a typical growth per cycle range of one Angstrom per cycle. Compositions can vary from metals to oxides, multilayer structures and even polymers via molecular layer deposition (MLD). Despite the extremely low deposition rates for well-known ALD coating process, such as for Al2O3, ALD can routinely deposit several tens of microns of material. Additionally, a methodology known as “spatial ALD” whereby the sample moves to different reaction zones (versus temporal ALD where the reactions are purged in/out of a chamber containing the sample) can allow for higher throughput and the opportunity for continuous ALD deposition. While many of the limitations of ALD regarding ultra-thin layers and slow processing are being addressed, non-semiconductor industrial applications of ALD are somewhat limited and remain more of an emerging area. ALD procedures and compositions for applications in modern aerospace technologies are needed.